Air energy reduction method and apparatus using waste heat from condensers or other low grade heat

ABSTRACT

The present invention provides a process for utilizing waste heat released by condensers of conventional air conditioning systems and more particularly using this low grade heat or other low grade sources that are slightly above ambient air temperatures to alter concentration of a liquid desiccant that contacts an ambient air stream thereby reducing its relative humidity while its temperature is controlled and generally reduced by heat exchange with another air stream that is saturated with water.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/204,705, filed Jan. 9, 2009.

FIELD OF THE INVENTION

The present invention relates to a process for utilizing waste heatreleased by condensers of conventional air conditioning systems and moreparticularly using this low grade heat or other low grade sources thatare slightly above ambient air temperatures to alter concentration of aliquid desiccant that contacts an ambient air stream thereby reducingits relative humidity while its temperature is controlled and generallyreduced by heat exchange with another air stream that is saturated withwater.

BACKGROUND OF THE INVENTION

Concerns related to expanding utilization of electrical energy alongwith related cost issues have caused increased interest in energyefficiency. A related concern is limiting emissions from electricalgenerating plants owing to greenhouse gas issues. A further concern isan economical means to dehumidify and cool outside air before itsinjection into interior spaces. Historically, needs to meet additionalair conditioning requirements have been met by increasing application ofstandard compressor based systems, a technology that is nearly 80 yearsold. Other compressor-based methods have been contemplated. U.S. Pat.No. 7,340,912 by Yoho et al teach placing a dedicated compressor withthe evaporator in one air stream and the condenser in another.Combination of a separate compressor-based heat pump with a revolvingsolid desiccant impregnated wheel is taught by Maeda et al in U.S. Pat.No. 6,205,797 Rejected heat from the heat pump is used to partiallyevaporate water absorbed by the wheel. Operation of these wheels isadiabatic meaning that the energy of the air remains constant thusmoisture removal is accompanied by an increase in heat. A separateheated stream of air is employed to remove absorbed moisture from thewheel. Use of revolving desiccant wheels desiccant is taught mostrecently in U.S. Pat. No. 7,338,548 to Boutall which adds that the airstreams are in heat exchange with each other. Also using two airstreams, Forkush et al in U.S. Pat. No 6,976,365 describes a dedicatedcompressor where the condenser and evaporator have separate air streamsto either absorb or reject moisture from a liquid desiccant. Anotherform of cooling and dehumidification is the absorption chiller operatingon pressures and vacuums that requires regeneration at high temperature,approximately 180 degrees F. with the heat generally supplied by fossilfuel. The major disadvantage of the existing technologies is that all ofthem require a dedicated thermal input in order to be functional. Apractice that would reduce energy utilization of these devices would beto possibly bring operating temperatures of the devices into closerproximity. For instance, a general heat and mass transfer device thatallows for improved temperature approaches of gas streams is taught byAlbers et al in U.S. Pat. No. 4,832,115. Another device operating atcloser temperature approximations is taught by Maisotsenko et al in U.S.Pat. No. 4,350,570. The apparatus employs an air stream of generally lowhumidity and is divided into primary and secondary flows with oneserving to cool a separate condensation element.

SUMMARY OF THE INVENTION

In view of the foregoing energy utilization disadvantages inherent inthe known methods to provide dehumidification and air temperaturereduction, the present invention offers closer proximities of heat andmass transfer throughout all of its steps allowing employment of lowgrade waste energy as is available from existent air conditionercondensers that have not been specially dedicated to the process or, asan example, from low grade solar means such as air heating devices.

The novel features as disclosed in the present invention, which will bedescribed subsequently in greater detail, can be best established byfirst employing a limited discussion of air properties representedherein. Reviewing temperatures exiting conventional compressor-based airconditioners it is found that while there is variance in these exhausttemperatures, many industry sources place the rise at only 15° F. Whileseemingly small this change can have a substantial effect on therelative humidity of air. For instance, at an American test condition(ARI-A) temperatures are established at 95° F. dry bulb and 75° F. wetbulb resulting in a relative humidity of 40%. By increasing the dry bulbtemperature to 110° F., when using heat generated by an air cooledcompressor, allows reduction of relative humidity to 25 percent, areduction of slightly less than 40 percent. Also of importance in theprocess of the present invention is the water saturated wet bulbtemperature of the air which in this case is 75° F. In this environment,possible operational parameters would be conditions where the maximumrelative humidity reduction to an ambient air stream would not fallbelow 25 percent and the maximum temperature reduction would be limitedto 75° F. An air stream also contains mass component that is expressedas moisture contained within the air. This can be articulated as poundsof water per pound of air or a volume of a cube measuring approximately2.5 feet per side. At the maximum conditions expressed above, air wouldcontain 0.014 pounds of water per pound of air. At the minimumconditions the air holds 0.0046 pounds of water per pound of air. Werethis air then saturated with water its temperature would be 55° F. Theheat (temperature) and the moisture content (mass) make up in generalterms the energy contained in the air. In the imperial system this isexpressed as British Thermal Units or Btu. At the maximum conditionsthis is 38.4 Btu per pound of air while the delivery condition would be23 Btu per pound of air. Given the significantly reduced humidity of thesupply air, this air may be injected into the interior building space toassist dehumidification of this space or could be nearly saturated atdelivery in order to be in correspondence with the normal deliveryconditions of compressor-based air conditioners. On a theoretical basisthe delivery conditions obtained by the present invention at the ARI-Atest conditions would equal the delivery conditions achieved byconventional compressor-based air conditioners.

The present invention combines dehumidification by employing a liquiddesiccant and cooling by means of heat exchange with a saturated airstream in a staged manner that allows for close temperature approaches.The invention is generally carried out through utilization of three airstreams. The first ambient air flow is augmented in temperature by a lowtemperature waste heat source. In many cases this air exits from an airconditioner condenser if the condenser is air cooled or air in heatexchange between the liquid desiccant and the hot water source by meansof liquid-to-liquid heat exchangers if the condenser is cooled withwater. The amount of heat rejected to the condenser is equal to thecooling capacity of the air conditioner plus the heat generated by theinefficiency of the compressor system, an amount equal to at least 10percent of the cooling capacity. This heated air can evaporate waterfrom a liquid desiccant owing to its reduced relative humidity. Thisregeneration air stream is exhausted to the environment at the sameenergy content as at its entrance but with at a lower temperature andwith a higher moisture level. The liquid desiccant then contacts aseparate ambient air stream, known as the supply air stream, and afterremoving moisture from this air stream is returned for regeneration. Asthe desiccant removes moisture from this supply air stream the energy ofthis air stream remains constant with the energy removed by moisturedeleted balanced by energy related to its rise in temperature. Theeffect of this temperature increase of this supply air is mitigated byutilization of a third air stream that is maintained in a near saturatedcondition, in this case substituting moisture for heat. This air streampasses counter-currently in a staged manner and the cooled water, cominginto balance with the reduced temperature caused by water evaporationinto the air stream, is in liquid-to-liquid heat exchange with theliquid desiccant. Heat is then exchanged between the liquid desiccantand the supply air flow owing to direct contact. Heat of dehydration ofthe supply air is mostly transferred to this saturated air stream anddepending on its wet bulb temperature most likely will reducetemperature of the supply air to less than ambient air conditions. Thistemperature reduction causes the relative humidity of the air toincrease thereby increasing the effectiveness of moisture removal by theliquid desiccant.

The heat and mass of each air stream should not be mixed during passagethrough the device of the current invention as when in heat exchangewith another air stream the driving force or temperature differentialbetween air streams would be significantly reduced. As an example, anair stream with entering temperatures of 90 degrees F. and transferringheat providing an exit air temperatures of 70 degrees F. would have an aaverage temperature of 80 degrees F. Were two stages employed, theaverage of the uppermost stage would be approximately 85 degrees F. andthe lower stage 75 degrees F. thus providing both higher and lowertemperature heat exchange possibilities. Without staging, the moisturecontent of an air stream would be blended thus averaging relativehumidity of an air stream as well as its temperature. This mixing islargely prevented in the process of this invention and is provided bythe development of stages, each with unique properties of heat and mass.Each stage contains a basin that is connected to a separate pump. Thepumped basin liquid from a supply air stage is directed through aliquid-to-liquid heat exchanger that exchanges heat with a correspondentliquid from a saturated air stage. After passage through theliquid-to-liquid heat exchanger caused by a dedicated pump, liquids aredistributed upon media such as that found in evaporative coolers or insmall cooling towers where the liquids are in contact with the air flowbefore falling into the basin thereby providing contact between theliquid and the air stream. A small stream of desiccant is allowed toflow between stages of the supply air stream before its return tocontact the regenerative air stream. This heated regenerative air streamis likewise segregated into stages in order that each stage can maintainits own temperature and relative humidity composition. In the samemanner as in the supply air stream, a small flow of desiccant is allowedto course counter-currently to the air stream with the air stream beingfirst in contact with the coolest and highest relative humidity airprogressively flowing to contact the highest temperature of the airstream that has the lower relative humidity.

It is to be understood that the invention is not limited in itsapplication to the details of construction for operation at atmosphericpressure as presented or at other pressures or vacuums, and to thearrangements of the components, set forth in the following descriptionor illustrated in the drawings. The invention is capable of otherembodiments, especially as related to utilization of other heat sourcesgenerally described as “waste heat” or use of other forms of heatingsuch as provided by solar air heaters along with the ability to storeconcentrated desiccant for evening uses as would be especially useful inmost solar applications, all of which might be carried out in variousways. Also, it is to be understood that the phraseology and terminologyemployed herein are for the purpose of the description and should not beregarded as limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the drawings:

FIG. 1 is a plan view with a portion of its cover removed of a deviceaccording to the present invention showing major components with certainof these shown schematically; and

FIG. 2 is a cross-sectional view taken along lines 2-2 of FIG. 1 withportions including connecting pasts thereto shown schematically.

DETAILED DESCRIPTION

The apparatus for implementing the invention consists of a stagedregenerator for removing moisture from a liquid desiccant, a staged airdehumidifier and cooler removing moisture from an air stream, and astaged saturator that maintains an air stream in a near saturatedcondition while exchanging heat with the dehumidifier and cooler. Thesethree modules are generally placed in a horizontal position and they maybe stacked one on the other or they may be physically separated fromeach other as long as they are thermally connected thermally or by meansof a flow of desiccant. Each module consists of a number of stages witheach stage consisting of wetting media, dedicated basin, pump and accessto a liquid flow. The stages in two of the modules are thermallyconnected by liquid-to-liquid heat exchangers and two modules areconnected by desiccant flow. Each module contains an air movement meansthat allows a supply of air that is separate from the other moduleswherein the flow through each module may be different in each module.

Referring descriptively to the drawings for mechanical function, inwhich similar reference characters denote similar elements throughoutthe several views, a device of the present invention is generallyindicated as device 11 in FIG. 1 and FIG. 2. The plan view of device 11as shown in FIG.1 depicts the configuration of each of the three modulesdesignated as modules 60, 70 and 80 in FIG. 2. Configuration isgenerally the same for each module allowing for common designations.Device 11 is schematically shown as rectangular with each of modules 60,70, and 80 having side walls 21 and 22, end walls 23 and 24, top wall 25(partially removed in FIG. 1) and bottom wall 26. If desirable, thewalls in thermal contact with ambient conditions may be thermallyprotected with insulation 27 that may be any efficient and highly vaporand liquid resistant material. Chamber length, height, and widthdimensions are generally consistent throughout the modules of device 11although the modules could be of different dimensions and each may varyalong their length. Materials may be of metal such as steel sheet oraluminum, or made in part from a rigid plastic. It is apparent from theabove description that the modules may be stacked or positioned at somedistance from each other and positioned directionally independently ofeach other as long as, where appropriate, thermal correspondence betweenstages and liquid desiccant flow between modules is maintained.

Basins 30 are utilized for liquids present in modules 60, 70, and 80.These basins are each segmented into at least two stages, with fourbeing shown in FIG. 1 as stages 31, 32, 33, and 34 of basin 30. Theeffective separation of temperatures and relative humidityconcentrations is generally increased by augmenting the number ofstages. Pipe 35 is located at the terminus of stage 31 while pipe 36 islocated at the terminus of stage 34. Liquids associated with the stagesare largely contained within stages; for instance within stage 31 bywall 37 having an opening provision 38 for staged-flow between stages aslocated between stages 31 and 32, 32 and 33, and 33 and 34 of basin 30.The opening provision may be a slit in wall 38 or maybe a tube insertedin wall 38. Basins 30 are normally molded from a high temperaturewithstanding plastic or FRP to avoid seams but could be of a strongermaterial depending upon structural requirements. The profile of thesebasins generally includes surface area 40 to collect liquids, a sump 41,A pump 42 is dedicated to each stage and is generally placed external tosump 41 and connected by pipe 43 to sump 41 or may be located withinsump 41. The pumped liquid first passes from pump 42 via pipe 44 ofmodule 60 to heat exchanger 45. The liquid-to-liquid heat exchangers maybe of standard configuration such as shell and tube, or plate and frame.Flow from liquid-to-liquid heat exchanger 45 is directed by pipe 46 toliquid discharge assembly 47 of module 60 that distributes basin liquidonto media 48 that is supported by open grid 49. Liquid thus distributedfalls through media 48 by gravity into basins 30. Materials withaugmented surface suitable for media 48 include that typically found inevaporator cooler products, small saddles or rings found in smallercooling towers, or other suitable material. View of one type of liquiddischarge assembly 47 found adequate for distribution is presented ineach stage of device 11 of FIG. 1 and has been designed so that liquidflow is nearly evenly distributed over the media surface with any biascounter to the air flow. Assembly 47 which is generally the same inmodules 60, 70, and 80 may incorporate additional distribution tubes orother means to improve disposition of the liquid. The pipes may be ofsuitable plastic material with spaced openings 50 cut into the liquiddischarge assembly 47 along its top surface in a “v” shaped pattern orthese spaced openings could contain low pressure nozzles inserted intoassembly 47. Liquid desiccant enters and exits basins 30 via pipes 35and 36 of module 60 moving counter-currently to an air stream flowingthrough module 60 directionally moving from basin 34 to basin 30 withair flow shown by arrow 61.

Thermal connection between the correspondent stages of modules 60 and 70is via liquid-to-liquid heat exchanger 45. Liquid from basin 30 ofmodule 70 flows through pipe 53 to pump 42 of module 70 and from pump 42to liquid-to-liquid heat exchanger 45 by means of pipe 55 where theliquid flows counter-currently to liquid passing from pipe 43 to pipe46. The liquid exits liquid-to-liquid heat exchanger 45 through pipe 56then discharged into liquid discharge assembly 47 of module 70.Correspondence between stages 31′ through 34 of module 60 and 31 through34 of module 70 are maintained with like stages of module 70 by means ofcounter-current liquid flows through the corresponding liquid-to-liquidheat exchanger 45. Water generally enters and exits basins 30 via pipes35 and 36 of module 70. The directional flow of the water relative to anair stream flowing through module 70 is significant only in thattemperature differential between the water and the air stream isgenerally minimized if the water and air flow designated by arrow 71 iscounter-current. In other configurations water could be directlyinjected into each stage however flow through all stages is preferred asan overflow at the exit prevents mineral accumulations. The direction ofair flow 71 of module 70 is counter-current to air flow 61 of module 60.

Dilute liquid desiccant flows from pipe 36 of module 60 to module 80,the desiccant regenerator, by means of pipe 36 located thereto to stage34. An air stream, shown by arrow 81, flows counter-currently to theliquid desiccant flow which exits stage 31 via pipe 35 of module 80 thatconnects by means of pump 82 with pipe 35 of module 60. The constructionand features of the stages of module follows that earlier describedincluding pathway 38 allowing liquid connection throughout the length ofmodule 80. In preferred embodiment of the present invention air stream81 passing through module 80 is generated and heated by an air cooledcondenser of an air conditioning system. Heated air from other sources,such as solar or waste heat air heaters could likewise be employed.Alternatively, a heated water stream, such as found in larger commercialair conditioners or from other sources or other heated liquids could beutilized. In this mode of operation a series of liquid-to-liquid heatexchangers, again illustrated by the numeral 45, could be employed withthe highest temperature water entering the liquid-to-liquid heatexchanger associated with stage 31. The liquid desiccant flow pattern isthe same as presented for module 60. Heat exchange is by means of pipes55 and 56 flowing liquid counter-currently to the liquid desiccant flowthrough liquid-to-liquid heat exchanger 45. Pipe 56 exitingliquid-to-liquid heat exchanger 45 of a stage connects with pipe 55 inthe next stage allowing for the stream of hot liquid to be counter-flowto the stream of air throughout the stages of device 80. With themodules placed as displayed in FIG. 2, the flow of liquid desiccant maybe by gravity from module 60 to module 80 with concentrated liquiddesiccant returned from module 80 to module 60 by means of pump 82 orthe function of pump 80 may be assumed by a pump already existent inmodule 80. Other arrangements of the modules in relationship to eachother may require alternate placement of gravity discharge and liquiddesiccant pumping activities.

The advantage of employing stages in order to obtain close proximity ofair temperatures and improved management of air relative humidity can beshown by presenting a calculated example, employing ambient conditionspreviously presented. Accepting an air cooled condenser and a rise aboveambient temperature of 15° F., air conditions would be 110° F. dry bulb,79° F. wet bulb with a moisture loading of 0.0141 pounds of moisture perpound of air, energy of 42 Btu per pound of air, and a relative humidityof 25%. Assuming a compressor-based air conditioner of one ton (12,000Btu) output, heat available to the regenerator would be 13,200 Btu.Given the 15° F. temperature rise, air needed to remove heat from thecondenser would 3,670 pounds as the air stream moisture content change,as determined from psychrometric tables, would be 3.6 Btu per pound ofair. Assuming air leaving the regenerator at 50% relative humidity inthe fourth stage, water removed by evaporation per pound of air would be0.0035 pounds with air exiting the regenerator at 94° F. At 3,670 poundsair per hour water removal would be 12.8 pounds with the equilibriumvalue of the liquid desiccant exiting the regenerator equal to an airstream of 30% relative humidity. Looking to the air dehumidification andair cooing module, Air delivery temperature of 85° F. would beobtainable given the ambient wet bulb being 75° F. in heat exchange withthe saturated air stream of module 70. Relative humidity could bereduced to 35% resulting in a moisture reduction from 0.0141 to 0.009 ora reduction of 0.0051 pounds of moisture per pound of air. Regeneratorremoval of 12.8 pounds divided by 0.0051 develops an air flow of 2,500pounds of air per hour. Energy reduction would be 38.4 less 30.4 or 8Btu per pound of air that when multiplied by 2,500 pounds of air perhour yields a computed value of 18,300 Btu of energy reduction, anamount adding 150% to the original compressor-driven cooling capacity of12,000 Btu per hour.

Elimination of the staged approach results in average temperaturesobtained in each module Instead of 16° F. temperature differential inmodule 80, the average of 8° F. might be obtained yielding an air streamwith a relative humidity of 32% compared with 25%. The saturated airstream of module 70 would have average temperatures of 79° F. comparedwith 75° F. when staging. Given the same driving force differentials,air delivery conditions would be 89° F. and 42% relative humidity.Moisture removal would be reduced to one-third of former values (from0.0056 per pound of air to 0.0018) while energy reduction reduces by 60%from 8 to 3.5 Btu per pound of air; the changes rendering thisnon-staged approach to low temperature waste resource utilization tolose economic appeal.

As to further discussion of the manner, usage, and operation of thepresent invention, the same should be apparent from the abovedescription. Accordingly, no further discussion relating to the mannerof usage and operation will be provided. With respect to the abovedescription then, it is to be realized that the optimum dimensionalrelationships for the parts of the invention, to include variations insize, materials, shape, form, function, and manner of operation,assembly and use, are deemed readily apparent and obvious to one skilledin the art, and all equivalent relationships to those illustrated in thedrawings and described in the specification are intended to beencompassed by the present invention. Therefore, the foregoing isconsidered as illustrative only of the principles of the invention.Further since numerous modifications and changes will readily occur tothose skilled in the art, it is not desired to limit the invention tothe exact construction and operation shown and described.

1. Apparatus comprising: a first chamber containing a first air flow device forming a first air flow of ambient air through the first chamber; a second chamber containing a second air flow device forming a second air flow through the second chamber, the air flow countercurrent to the first air flow; a third chamber receiving a third air flow flowing through the third chamber from a compressor driven air conditioner condenser; the first chamber having a plurality of first stages, the stages containing a liquid desiccant, the liquid desiccant passing through each stage counter-currently to the first air flow while in contact with the first air flow in each stage; a second chamber having a plurality of second stages, the stages containing water, the water being in contact with the second air flow in each stage: the third chamber having a plurality of third stages, the stages containing a liquid desiccant, the liquid desiccant passing through each stage counter-currently to the third air flow while in contact with the third air flow in each stage; the first air stream dehumidified by the liquid desiccant, the liquid desiccant becoming dilute passing through the first chamber; the first stages of the first chamber in thermal association with the corresponding second stages of the second chamber by means of heat exchange between the liquid desiccant and water, the water receiving heat developed in the first chamber during dehumidification of the first air stream; and the dilute desiccant from the first chamber flowing to the third chamber, the third air stream receiving heat from the condenser causing evaporation from the desiccant passing through the third stages with the concentrated desiccant returned to the first chamber.
 2. Apparatus, comprising: a first chamber containing a first air flow device forming a first air flow of ambient air through the first chamber; a second chamber containing a second air flow device forming a second air flow through the second chamber, the air flow countercurrent to the first air flow; a third chamber containing a third air flow device receiving heat from a heat source forming a third air flow through the third chamber; the first chamber having a plurality of first stages, the stages containing a liquid desiccant, the liquid desiccant passing through each stage counter-currently to the first air flow while in contact with the first air flow in each stage; a second chamber having a plurality of second stages, the stages containing water, the water being in contact with the second air flow in each stage: the third chamber having a plurality of third stages, the stages containing a liquid desiccant, the liquid desiccant passing through each stage counter-currently to the third air flow while in contact with the third air flow in each stage; the first air stream dehumidified by the liquid desiccant, the liquid desiccant becoming dilute passing through the first chamber; the first stages of the first chamber in thermal association with the corresponding second stages of the second chamber by means of heat exchange between the liquid desiccant and water, the water receiving heat developed in the first chamber during dehumidification of the first air stream; and the dilute desiccant from the first chamber flowing to the third chamber, the third air stream receiving heat from the heat source causing evaporation from the desiccant passing through the third stages with the concentrated desiccant returned to the first chamber.
 3. A process, comprising: dehumidifying an ambient air stream in a staged manner by means of a liquid desiccant exposed to this air stream in each stage causing absorption of water from this air stream; transferring heat from this dehumidification to a another air stream exposed to water in a staged manner causing evaporation of water into this air stream in each stage; and subjecting the desiccant containing the absorbed water to a heated air stream in a staged manner to evaporate water from the desiccant in each stage. 